User's Manual

Repair steps:
1. Check if the headset can be detected by the phone after being plugged. If cannot, replace with a
new headset and verify again;
2. Check if the relevant components have soldering problems;
3. If you still have not found the problem, then check whether the U1 chip has soldering
or performance problems or not.
5.8. SIM card theory and repair
F9 has a built-in dual-card management chip, and has two SIM card connectors, supports dual
SIM dual standby.
Repair steps:
1. Check if the dual- cards’ insertion direction is OK;
2. Check if the card connector metal contact points have problems, such as existing foreign
matters or are rusting, etc;
3. Check if the SIM card connectors and components around have soldering problems;
4. If failed to find out problems, check whether U1 chips have soldering or performance
issues.
5.9. LCD display abnormity
F9 LCD backlight is directly drive by U1, without extra drive circuit. LCD data and control
lines connect to LCD interface through the capacitor, specific circuit as follows: